I've been doing this for 40 ys and the only time I've seen this happen is back in the days when we used bass and a torch. You didn't use a flux coated wire by any chance did you.

no flux core wire. welder is the same setup the guys use for all the shop collision work. theres not a lot of butt welding on there side that i see but we have never had anything come back because of ghosting issues. like i said if the panel had a factory-ish peel to it, it would hardly be noticeable. but when the panel is flat it stands out.